The preparation and properties of a solubilized respiratory complex from Escherichia coli

Abstract

1. 1. Treatment of the respiratory particle fraction from Escherichia coli with cholate in the presence of ammonium sulfate liberated a stable, soluble, cytochrome-containing moiety (“soluble respiratory complex”) of “molecular weight” of about 2×10 6. 2. 2. The soluble respiratory complex contained nonheme iron, ubiquinone, cytochrome b 1, cytochrome o, acid-resistant flavin and acid-released flavin in a ratio of 56:18:3.7:0.96:0.7:1. 3. 3. The soluble respiratory complex was devoid of NADH and succinate oxidase activities until ubiquinone isoprenologues were added. Ubiquinone Q-2 was the most effective derivative in restoring oxidase activities. 4. 4. Reactivation of succinate oxidase by Q-2 was produced by a 10-fold lower concentration than that required for NADH oxidase. 5. 5. Addition of Q-2 lowered the aerobic steady state level of cytochrome b 1 reduction in the soluble respiratory complex with succinate but not with NADH as substrate. The inhibitor 2- n-heptyl 4-hydroxyquinoline N-oxide (HQNO) increased this value with the former but not with the latter substrate. Thus, deficiency of ubiquinone and addition of HQNO give a similar effect on the succinate-reducible cytochrome b 1. 6. 6. It is proposed that in the soluble respiratory complex part at least of the cytochrome b 1 reducible by succinate is either on a side-branch from the main respiratory chain or that Q-2 interacts between succinate-reducible cytochrome b 1 and oxygen.